Fossil Discovery Has Implications For Patterns Of Evolution

The University of Toronto discovery of fossilized remains of a new species of giant ground sloth is challenging the theory of evolutionary change of fauna between North and South America.

Gerardo De Iuliis, a graduate and teacher in the department of zoology, and a Brazilian colleague discovered in Citrus County, Fla., fossilized skeletons of giant sloths that likely existed over two million years ago. "These giant sloths were among the earliest mammals and the largest to migrate from South America to North America after the formation of the Panamanian land bridge (present-day Central America)," he says. This species was later replaced by one called the Panamerican giant ground sloth which became extinct 10,000 years ago.

Current evolutionary theory suggests that mammals from South America were inherently inferior to and could not survive as well as their North American counterparts. "The discovery of this new species of giant sloth has significant ecological implications for this traditional theory," De Iuliis says. "These groups of sloths migrated to North America, diversified and thrived for nearly two million years which would hardly be expected for a group of inferior animals. A similar pattern can be noted for other South American mammals."

The giant ground sloth, on average the size of a small elephant, weighed about four tons and is believed to have been a herbivore. They had huge claws -- much larger than those of their modern-day tree sloth cousins -- and were probably capable of walking on their hind legs. A study, co-authored by De Iuliis, has recently been published in the Zoological Journal of Linnean Society.